Ultrasonic transducers of this type are used in ultrasonic sensors in motor vehicles, for instance as parking aid. These sensors are generally made up of a housing, which accommodates a diaphragm cup in whose interior a transformer element is disposed. The transformer element (e.g., a piezo element) is mounted on the bottom of the diaphragm cup, the bottom also being referred to as diaphragm. In the installed state, the outer surface of the diaphragm is exposed and excited by the transformer element for the emission of ultrasonic waves. Furthermore, it receives the ultrasonic waves reflected off an object. The ultrasonic transformer is situated inside the housing in such a way that the greatest low-acoustic impedance decoupling is obtained. The ultrasonic sensor is installed in a suitable vehicle section, e.g., in a shock absorber, with the aid of a receptacle that likewise has a decoupling function.
The fixation of the diaphragm cup in the housing is realized by, for example, a first inner decoupling ring, as it is referred to, which at least partially encloses the diaphragm cup and is joined to the housing via a holding sleeve mounted thereon by clipping, for example. A second decoupling ring mounted on the diaphragm cup forms a support in the associated vehicle section. The decoupling rings are made from a damping material such as silicon. Disadvantageous in this context are the number of parts and the production/assembly expense.
In another development, instead of being provided with the inner decoupling ring, the housing is filled with a damping material for the inner suspension of the diaphragm cup. One possibility in this context is an injected filler or damping material of silicon. Such a form-locking bond has been tried and tested but the associated production time and expense is disadvantageously high. For example, the extrusion coating with the damping material requires a tool that seals in a downward direction, i.e., to the side of the exposed diaphragm of the diaphragm cup, which tool must enclose the diaphragm cup and the housing in form-locking manner until the extrusion-coated damping material, e.g., a vulcanization, has hardened completely. This sealing tool has to bridge a gap between the diaphragm cup and the wall of the housing, which has a minimum thickness, in order for the diaphragm cup to exhibit the low acoustic impedance decoupling once the housing has been extrusion-coated. In addition, following the vulcanization, a cutting tool has to remove the last traces of the extrusion coat at the edge to the diaphragm cup before the second decoupling ring is able to be mounted. Apart from the production time, the fact that such tools are relatively expensive constitutes a disadvantage.
One example to illustrate this is described in German Patent Application No. DE 197 55 729 A1, which describes an ultrasonic sensor having a housing with a plug-in connection, an ultrasonic transducer, and a circuit board, the housing being subdivided into a support and a surrounding protective cover. A decoupling ring is provided to mount the ultrasonic transducer inside the housing in sealing and vibration-damped fashion. A casting compound completely fills up the ultrasonic transducer and forms a mechanically durable and tight encapsulation of the ultrasonic sensor.